A ratio is an expression which compares quantities relative to each other. The most common examples involve two quantities, but in theory any number of quantities can be compared. Mathematically they are represented by separating each quantity with a colon, for example the ratio 2:3, which is read as the ratio "two to three". AND
A rate is a special kind of ratio, indicating a relationship between two measurements. A rate may be defined using two numbers of the same units resulting in a dimensionless quantity (for example, "1 in 10 people"), or may be defined by two different measurements with different units (for example, "meters per second" used in speed).